Apparatus for the wet-screening of particles



Nov. 21', 1967 J. N. J. LEEMAN 3,353,674

APPARATUS FOR THE WET-SCREENING OF PARTICLES Filed July 27. 1964 UnitedStates Patent APPARATUS FOR THE WET-SCREENING 0F PARTICLES Jan N. J.Leeman, Heerlen, Netherlands, assignor to Stamicarbon N.V., Heerlen,Netherlands Filed July 27, 1964, Ser. No. 385,224 Claims priority,application Netherlands, Aug. 1, 1963, 296,114 6 Claims. (Cl. 209-440)The present invention relates to a screening apparatus for thewet-screening of particles and more particularly to improved apparatusof the tangentially fed, fixed bar screen type. Apparatus of this type,which is sometimes designated a sieve bend, comprises a stationary,cylinrically curved screening deck provided with .a supply end, adischarge end, and a screening surface extending between them and beingprovided with a large number of transversely extending screen openings.The particles and the liquid to be separated are fed tangentially, as alayer, on to the concave side of the screening deck at an initial ratehigh enough to make an overflow fraction move from the supply end to thedischarge end. As the layer travels over the screening surface,successive thin laminae of a thickness considerably less than the widthof the screen openings are peeled off; the liquid and the particleswhich have a diameter smaller than the width of the openings passthrough the openings as undersize.

A preferred embodiment of the sieve bend apparatus has a screeningsurface which consists of a large number of parallel bars settransversely t0 the direction of flow. These bars may be generallyrectangular in transverse cross section. Accordingly they are mounted soas to have faces which are presented towards the supply end of thescreening deck and which split oh the successive thin laminae to producethe sieve bend effect. If the particles in the liquid being screened aresomewhat abrasive, the bar face edges become somewhat rounded in thecourse of time, which results in a decrease of the screening elliciency.Usually, to increase the useful life of the screening deck at areasonably high screening efficiency, the bars and the deck are madesymmetrical, so that upon reversal of the screening deck the desiredlamina splitting can be effected by the faces of the bars which wereoriginally presented towards the discharge end. The length of the periodbetween reversals depends on the material of which the screening deck ismade and on the abrasiveness and volume of the influent particle-liquidmixture to which it is subjected.

The width of the inlet of most currently used sieve bend installationsis generally made so large that it equals three times the maximum grainsize of the raw product supplied thereto. By using a slot width of thissize, obstruction of the slot is effectively prevented. However, thisoften causes the coarser particles flowing along the upper surface ofthe raw product to be delivered to the screening deck so far below thesupply end of the deck that not only will these particles fail to hitthe screening deck at a tangent to the deck resulting in thediscrimination being shifted to a larger particle size than is-desired,but also there will be additional wear of the screening deck at thepoint where these particles hit the deck. As a consequence, the life ofthe deck is shortened.

To alleviate this shortcoming, it has been suggested, for instance inUS. Patent 3,007,574, to provide a b-aflle system as a part of the inletto the screening device. However, such a system has not been found to heacceptably satisfactory in many instances because the baflles rapidlybecome Worn and thus ineffective and they substantially increase theoverall height of the screening installation.

It is therefore an important object of the present in- 3,353,674Patented Nov. 21, 1967 vention to provide a sieve bend installationwhich does not possess the above mentioned drawbacks and is particularlysuited for handling coarse particles.

It is another object of the invention to provide screening apparatus ofthe type described wherein the feeding arrangement for the screeningdeck consists of a feeding launder at one end of the bottom of which isa downwardly opening slot-like spout which is inserted in a throatdefined between a fixed downwardly sloping wall tangentially leadinginto the screening surface and by a flexible movable wall for varyingthe width of the throat passage. The vertical distance between the saidslot-like spout and the upper end of the screening surface according tothe invention is large and adjustable to ensure the desired screeningeffect.

A moregeneral object of the invention is the provision of an extremelysimple, easily accessible, and conveniently arranged sieve bendconstruction, in which the screening deck is subjected to uniform wearand the overall height is minimized owing to the elimination of thenecessity of providing a feeding trough with baffles in suchinstallations to ensure the desired separation.

The invention will now be elucidated with reference to the illustrativeembodiment shown in the attached drawing.

In the drawing:

FIGURE 1 is a vertical longitudinal sectional view of the sieve bendinstallation according to the invention;

FIGURE 2 is a fragmentary vertical longitudinal sectional view of thesieve bend showing a modified arrangement of the feeding launder.

Now with more specific reference to the drawings the open feedinglaunder 1 is provided near one end of the bottom thereof with a spout 2communicating with a throat 3 of the sieve bend, generally indicated at4. The throat 3 is defined by a fixed, sloping wall 5 tangentiallyleading into the uper end of the curved screening deck 6 of the sievebend 4 and by a movable wall comprising a resilient rubber plate 7, insuch a way that the wall-5 and the plate 7 converge downwardly towardsthe sieve bend 4. In order to take advantage of the increased efficiencyprovided by the flexible plate 7 and more smoothly tangentially transferthe influent particle containing liquid to the screening deck 6, thewall 5 is preferably set at an angle in the range of 60 to fromhorizontal.

Instead of being made of rubber, the plate 7 may alternately be made ofother tough, flexible wear resistant material such as synthetic plasticsheet material. By preference, the upper edge of the plate 7 is clampedat an angle to the vertical, although a hinged attachment is also withinthe purview of the invention. The plate 7 effectively ensures thatliquid and solid particles which might otherwise detach themselves fromthe layer flowing along wall 5 will be tangentially supplied to thescreening deck 6. Furthermore the generally rectangular throat end atthe lower end of the fixed sloping wall 5 and the lower end of the plate7 will always adjust itself to the minimum area which will pass theinfluent particle containing liquid owing to the resilience of the platematerial. The just mentioned feeding throat never being unnecessarilywide, the liquid will always be supplied in a direction more nearlytangential to the screening deck than was heretofore practicable thuspromoting a more even wear of the deck and more effective separation ofthe particles by size. As the rubber plate 7 is deflectable, obstructionof the feeding throat by coarse particles contained in the materialsupplied will not occur.

The screening deck 6 is preferably mounted so as to be reversible byturning it end for end to extend the life thereof. The underflowfraction of the sieve bend 4 which passes in laminae between the barsthereof is collected in a collecting reservoir 8, which is communicatedfreely with the atmosphere along an upper portion of a side thereof. Thecollected underflow fraction is discharged from the reservoir 8 througha suitable conduit (not shown). The overflow fraction of the sieve bend4 carrying the larger diameter particles is discharged via the slopingoverflow plate 9. The plate is preferably positioned at a delivery angleof about 30 from horizontal.

The bottom of the feeding launder 1 may slope towards the sieve bend ata small angle (a few degrees) in order to facilitate movement of the rawproduct therein. As illustrated, launder 1 including the spout 2 issuspended over the throat by means of a detachable connection shownincluding a plurality of relatively long bolts 10. By means of thesebolts the launder 1 can be leveled to obtain a supply fiow which isproperly distributed across the width of the spout. The bolts 10additionally enable the chute to be adjusted vertically. The verticaldistance between the opening 2 and the upper end of the screeningsurface 6 being adjusted empirically to ensure the desired screeningeffect. In practice, this distance may be about 0.5 meter.

If space limitations or other circumstances so demand, the launder mayalternately be connected to the sieve bend installation the other wayround as shown in PEG- URE 2. This can be done in a simple way byreleasing the bolts 10, lifting the launder spout out of the throat andturning it through 180 in the horizontal plane with respect to thethroat. The performance of the screening device according to theinvention does not depend on the direction in which the material issupplied, because of the sloping wall 5 and the convergence and crosssectional area adaptability of the throat 3.

The walls of the launder, the spout 2, and the fixed sloping walls 5 and9 are lined with wear-resistant material.

It should now be apparent that the screening apparatus of the inventionjust described effectively accomplishes all of the objects set forthhereinabove. However, inasmuch as the specific embodiment shown anddescribed to illustrate the principles of the invention may beconsiderably modified without departing from these principles, thepresent invention should be understood as encompassing all modificationsWithin the spirit and scope of the following claims.

I claim:

1. In an apparatus for the wet-screening of solid particles comprising asloping concavely curved sieve bend screening surface and a feedingdevice suprajacent said sieve bend an adapted to direct a downwardlyfalling layer of particle containing liquid tangentially onto said sievebend, the improvement wherein said feeding device includes:

(a) means defining a throat comprising a fixed position sloping wall anda movable wall spaced outwardly from and sloping downwardly toward saidfixed wall, said movable wall being composed of a plate of resilientflexible material fixedly clamped at the upper end thereof at asubstantial angle to the vertical; and

(b) a feeding launder for receiving particle containing fluid, saidlaunder being mounted above said throat, said launder having, atransversely elongated spout communicated thereto, said spout dependingdownwardly from said launder toward said throat.

2. Apparatus as set forth in claim 1 wherein the improvement furtherincludes connector means on the apparatus for vertically adjusting saidfeeding launder with respect to said throat to provide means forempirically adjusting the separation provided by said sieve bend.

3. Apparatus as set forth in claim 1 wherein the sloping angle of saidfixed position sloping wall is in the range of to to a horizontal plane.

4. Apparatus as set forth in claim 1, the improvement additionally,including an overflow plate leading tangentially from the lower extentof the sieve bend screening surface and positioned at an angle of about30 to a horiozntal plane.

5. Apparatus as set forth in claim 1, the improvement additionallyincluding an underflow collecting reservoir mounted beneath said curvedsieve bend screening surface, said reservoir being communicated to theatmosphere.

6. Apparatus as set forth in claim 1 wherein the improvement furthercomprises connector means on the apparatus detachably mounting thefeeding launder therefrom; said connecting means further allowing therernounting of said feeding launder on said apparatus in a positionrotated degrees in a horizontal plane from the predetachment positionthereof.

References Cited UNITED STATES PATENTS 1,333,127 3/1920 Nall 209262 X2,916,142 12/1959 Fontein 209274 2,995,245 8/1961 Titelboorn 209243 X3,007,574 11/1961 DeKoning 209281 K 3,116,237 12/1963 Fontein et al.209242 3,145,164- 8/1964 Jonkman 209254 FOREIGN PATENTS 128,815 7/1959Russia. 566,362 4/ 1958 Belgium.

HARRY B. THORNTON, Primary Examiner. R. I-IALPER, Assistant Examiner.

1. IN APPARATUS FOR THE WET-SCREENING OF SOLID PARTICLES COMPRISING ASLOPING CONCAVELY CURVED SIEVE END SCREENING SURFACE AND FEEDING DEVICESUPRAJECENT SAID SIEVE BEND AN ADAPTED TO DIRECT A DOWNWARDLY FALLINGLAYER OF PARTICLE CONTAINING LIQUID TANGENTIALLY ONTO SAID SIEVE BEND,THE IMPROVEMENT WHEREIN SAID FEEDING DEVICE INCLUDES: (A) MEANS DEFININGA THROAT COMPRISING A FIXED POSITION SLOPING WALL AND A MOVABLE WALLSPACED OUTWARDLY FROM AND SLOPING DOWNWARDLY TOWARD SAID FIXED WALL,SAID MOVABLE WALL BEING COMPOSED OF A PLATE OF RESILIENT FLEXIBLEMATERIAL FIXEDLY CLAMPED AT THE UPPER END THEREOF AT A SUBSTANTIAL ANGLETO THE VERTICAL; AND (B) A FEEDING LAUNDER FOR RECEIVING PARTICLECONTAINING FLUID, SAID LAUNDER BEING MOUNTED ABOVE SAID THROAT, SAIDLAUNDER HAVING A TRANSVERSELY ELONGATED SPOUT COMMUNICATED THERETO, SAIDSPOUT DEPENDING DOWNWARDLY FROM SAID LAUNDER TOWARD SAID THROAT.